1. Field of the invention
This invention relates to digital radiographic image displays and more particularly to the use of an asymmetrical marker to determine the proper orientation of a displayed digital radiogram.
2. Description of Related Art
In the past decade there has been great progress made in the area of direct radiographic imaging using detectors comprising a two dimensional array of minute sensors to capture a radiation generated image. Information representing an image is captured, often as a charge distribution stored in a plurality of charge storage capacitors in individual sensors arrayed in a two dimensional matrix. We will refer to such detectors generically as direct radiographic detectors to differentiate them from the often referred to as traditional radiographic detectors which employ a photosensitive film usually in combination with an intensifying screen to produce a photographic image of the incident X-ray radiation.
The direct radiographic detectors typically comprise a two dimensional array of sensors with associated switching and addressing circuitry built on an insulating substrate, usually a glass plate. U.S. Pat. No. 5,319,206 issued to Lee et al. on Jun. 7, 1997, shows a typical direct radiation detector comprising an array of sensors for the generation and capture of charges following exposure to X-ray radiation. Readout of the stored charges is accomplished in any one of a plurality of manners. U.S. Pat. No. 5,648,660, also by Lee et al. discloses a method for the readout of stored charges in a direct radiographic imaging panel.
Direct radiation detectors offer a number of distinct advantages over the traditional film methods. The availability of a radiogram in electronic signal format, permits the use of digital signal conversion and all the advantages of signal storing, retrieval, transmission and processing associated with digital imaging.
This availability of the image in digital format, however, at times presents certain problems. For instance a captured digital image is stored in the form of a plurality of pixel values. These values undergo a number of operations as part of the system image processing routines, and such operations often include image rotation to present the image in xe2x80x9cportraitxe2x80x9d or xe2x80x9clandscapexe2x80x9d format for instance and may involve in addition to rotation, image mirroring, a process where the image is xe2x80x9cflippedxe2x80x9d front to back.
While this versatility presents a number of advantages, it is important to be always able to determine the original image orientation and original pixel location. This is particularly important when bad pixel correction must be applied. Such correction relies on pixel maps that correspond to the original image capture orientation as it applies corrections to the pixels corresponding to predetermined exact coordinates of detector elements. If the orientation of the image to be corrected is not the original, mapped bad pixels will not correspond to rotated image pixels.
A second reason for the need to know the original orientation of a radiogram is that when viewing a radiogram, such as a chest image, it is essential to know if the image has been flipped or not, as this places the internal organs in their proper position. This is important because a small minority of the population has their heart and other organs on the opposite side from the majority, i.e. heart is center right rather than center left, etc. The radiologist must be able to determine whether the displayed image has been mirrored or not, so that he knows whether he is looking at a front or a back view of the patient.
In traditional radiography this was done by physically marking one side of the film, such as by notching a corner of the film, or placing a piece of tape at one corner on one side of the film. This, however is not practical when there is no film present and the image is a sequence of a plurality of numbers stored in a memory. There is thus a need to develop a marker for a digital radiogram that will permit the easy identification of the image orientation at any stage of processing and display relative to the original image orientation as captured by the direct radiographic detector.
It is, therefore, an object of this invention to provide an orientation marker for a digital radiogram comprising a plurality of pixels arrayed along a plurality of rows and columns, the pixels having densities represented by digital values. The marker comprises a number of marker pixels arrayed along at least one row and one column. Each of these pixels has a marker pixel digital value which has been selected to form an asymmetrical marker pixel pattern on the radiogram. Preferably, the marker pixel values replace the original radiogram pixel values.
The desired asymmetry may be obtained in one of two manners or as is preferred by a combination of the two manners. It can be obtained by selecting the marker pixel digital values to form a unique, asymmetrical sequence of values that can only be retrieved (or its density pattern observed) when the digital values representing the radiogram are retrieved (or displayed) in a particular orientation, such orientation being almost always, the original orientation of the radiogram and corresponding image data. The marker asymmetry may also be obtained by the use of a particular selected marker geometry or as preferred, by a combination of pixel geometry and distinct values such as to obtain the desired asymmetry in readout and display of the marker which identifies the radiogram original orientation.
In order for the marker not to intrude in the diagnostic portion of the radiogram, the marker is preferably placed adjacent an upper left hand corner of the digital radiographic image. Still more preferably the marker may be shaped as an xe2x80x9cLxe2x80x9d having a pixel common to a row and a column of the rows and column comprising the marker, and the marker common to both such row and column is a first pixel on a first row and a first column of the plurality of rows and columns of pixels forming the radiogram.
Viewed in a different way, the invention is an orientation marker comprising a number of marker pixels in a two dimensional array superposed on a digital radiogram comprising a plurality of pixels having digital values representing pixel densities. Each of the marker pixels has a value selected to form in combination with all the other marker pixel values a machine readable identification code when the digital values representing the radiogram (with the marker included) are read out to process the image data or to display the radiogram in its original orientation as captured by the detector.
This invention may also be viewed as a plurality of digital values representing a radiogram each of said digital values corresponding to a pixel arrayed along a plurality of rows and columns and representing said pixel density. A selected number of said digital values have imposed values selected to together, form a machine readable identification code when the radiogram digital values are read in an desired radiogram orientation.
The invention also comprises a process for identifying the proper orientation of a digital radiogram composed of a plurality of pixels each having a digital value representing image densities. According to this process a digital marker is placed on the captured digital radiogram by:
a) selecting a plurality of pixels along at least one row and at least one column to form an array of selected pixels;
b) selecting a plurality of digital pixel values
c) replacing the digital values of the plurality of selected pixels with the selected digital values to form an asymmetrical array of marker pixels.